1. Field of the Invention
This invention relates to a method of and a system for transferring a vehicle body to an overhead conveyor, and more particularly to a method of and a system for transferring a vehicle body which is through with the coating step to an overhead conveyor in a vehicle assembly line.
2. Description of the Prior Art
In assembly of a vehicle, a vehicle through the coatig step is generally conveyed from a coating line to a vehicle assembly line placed on a carriage, the vehicle body on the carriage is transferred to an overhead conveyor in the vehicle assembly line, and the vehicle body is equipped while it is conveyed by the overhead conveyor.
In such a vehicle assembly line, a conveyor provided with a hanger 2 having front and rear support arms 2a and 2b, as shown in FIG. 9, which are positioned on the front side and the rear side of the vehicle body 1 to support the lower side of the side sill of the vehicle body 1 has been used as the overhead conveyor. (For example, see Japanese Patent Publication No. 56(1981)-43963.)
However, recently, automation has been sharply promoted in the vehicle assembly line, and for example, the windowpanes of the windshield and the rear window come to be mounted by robots. The robots for mounting the windowpanes are disposed on the side of the assembly line, and when mounting the windowpanes, the robots stretches arms from the side of the assembly line. In the case of the conventional hanger 2 having the front and rear support arms 2a and 2b, the front and rear support arms 2a and 2b are positioned on the side of the windshield and the rear window of the vehicle body supported by the hanger 2, and the arms of the robots interferes with the support arms 2a and 2b upon mounting of the windowpanes. This gives rise to problems in automating mounting of the windowpanes.
In order to overcome such problems, it has been proposed as disclosed in Japanese Unexamined Utility Model Publication No. 59(1984)-22053 to use an overhead conveyor provided with an inverted-T-shaped hanger comprising a single vertical support arm and a horizontal support member which is fixed to the lower end of the vertical support arm to extend horizontally and supports the side sill of the vehicle body. In the inverted-T-shaped hanger, the vertical support arm is positioned on the side of the center pillar of the vehicle body, and no support arm exists on the side of the front and rear windows, and accordingly, windowpane mounting operation by the robots cannot be interfered with, thereby facilitating automation of the assembly line.
In the vehicle assembly line, there is sometimes employed "after-door-mounting system" in which the doors are once removed from the coated vehicle body, the doors and the vehicle body are separately equipped in separate lines, and the doors are thereafter mounted on the body again.
In the case the after-door-mounting system is emloyed, conventionally, the vehicle body through with the coating step is once transferred to the overhead conveyor in the assembly line, and after the overhead conveyor is lowered, the doors are removed from the vehicle body on the overhead conveyor.
However, in the case of the inverted-T-shaped hanger, the supporting arm in the side of the center pillar interferences with the door upon removal of the door, particularly in the case of two-door or three-door type vehicles, unlike the aforesaid hanger 2 having the front and rear support arm 2a and 2b spaced from each other before and after the door.
Accordingly, in order to further promote automation of the vehicle assembly line, it is preferred that the overhead conveyor having the inverted-T-shaped hanger be used in the assembly line while facilitating removal of the doors.